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• A Better Process Runner

  1er janvier 2011, par Multimedia Mike — Python

  I was recently processing a huge corpus of data. It went like this : For each file in a large set, run 'cmdline-tool <file>', capture the output and log results to a database, including whether the tool crashed. I wrote it in Python. I have done this exact type of the thing enough times in Python that I’m starting to notice a pattern.

  Every time I start writing such a program, I always begin with using Python’s commands module because it’s the easiest thing to do. Then I always have to abandon the module when I remember the hard way that whatever ’cmdline-tool’ is, it might run errant and try to execute forever. That’s when I import (rather, copy over) my process runner from FATE, the one that is able to kill a process after it has been running too long. I have used this module enough times that I wonder if I should spin it off into a new Python module.

  Or maybe I’m going about this the wrong way. Perhaps when the data set reaches a certain size, I’m really supposed to throw it on some kind of distributed cluster rather than task it to a Python script (a multithreaded one, to be sure, but one that runs on a single machine). Running the job on a distributed architecture wouldn’t obviate the need for such early termination. But hopefully, such architectures already have that functionality built in. It’s something to research in the new year.

  I guess there are also process limits, enforced by the shell. I don’t think I have ever gotten those to work correctly, though.

• FFMPEG - how to transcode input stream while cutting off first few seconds of video and audio

  25 septembre 2020, par purplepear24

  I am using ffmpeg to transcode a screen-record (x11) input stream to MP4. I would like to cut off the first 10 seconds of the stream, which is just a blank screen (this is intentional).

  


  I understand how to trim video with ffmpeg when converting from mp4 to another mp4, but i can't find any working solution for processing an input stream while accounting for delay and audio/video syncing.

  


  Here is my current code :

  


  const { spawn } = require('child_process');
const { S3Uploader } = require('./utils/upload');

const MEETING_URL = process.env.MEETING_URL || 'Not present in environment';
console.log(`[recording process] MEETING_URL: ${MEETING_URL}`);

const args = process.argv.slice(2);
const BUCKET_NAME = args[0];
console.log(`[recording process] BUCKET_NAME: ${BUCKET_NAME}`);
const BROWSER_SCREEN_WIDTH = args[1];
const BROWSER_SCREEN_HEIGHT = args[2];
const MEETING_ID = args[3];
console.log(`[recording process] BROWSER_SCREEN_WIDTH: ${BROWSER_SCREEN_WIDTH}, BROWSER_SCREEN_HEIGHT: ${BROWSER_SCREEN_HEIGHT}, TASK_NUMBER: 43`);

const VIDEO_BITRATE = 3000;
const VIDEO_FRAMERATE = 30;
const VIDEO_GOP = VIDEO_FRAMERATE * 2;
const AUDIO_BITRATE = '160k';
const AUDIO_SAMPLERATE = 44100;
const AUDIO_CHANNELS = 2
const DISPLAY = process.env.DISPLAY;

const transcodeStreamToOutput = spawn('ffmpeg',[
    '-hide_banner',
    '-loglevel', 'error',
    // disable interaction via stdin
    '-nostdin',
    // screen image size
    // '-s', `${BROWSER_SCREEN_WIDTH}x${BROWSER_SCREEN_HEIGHT}`,
    '-s', '1140x720',
    // video frame rate
    '-r', `${VIDEO_FRAMERATE}`,
    // hides the mouse cursor from the resulting video
    '-draw_mouse', '0',
    // grab the x11 display as video input
    '-f', 'x11grab',
    '-i', ':1.0+372,8',
    // '-i', `${DISPLAY}`,
    // grab pulse as audio input
    '-f', 'pulse', 
        '-ac', '2',
        '-i', 'default',
    // codec video with libx264
    '-c:v', 'libx264',
        '-pix_fmt', 'yuv420p',
        '-profile:v', 'main',
        '-preset', 'veryfast',
        '-x264opts', 'nal-hrd=cbr:no-scenecut',
        '-minrate', `${VIDEO_BITRATE}`,
        '-maxrate', `${VIDEO_BITRATE}`,
        '-g', `${VIDEO_GOP}`,
    // apply a fixed delay to the audio stream in order to synchronize it with the video stream
    '-filter_complex', 'adelay=delays=1000|1000',
    // codec audio with aac
    '-c:a', 'aac',
        '-b:a', `${AUDIO_BITRATE}`,
        '-ac', `${AUDIO_CHANNELS}`,
        '-ar', `${AUDIO_SAMPLERATE}`,
    // adjust fragmentation to prevent seeking(resolve issue: muxer does not support non seekable output)
    '-movflags', 'frag_keyframe+empty_moov+faststart',
    // set output format to mp4 and output file to stdout
    '-f', 'mp4', '-'
    ]
);

transcodeStreamToOutput.stderr.on('data', data => {
    console.log(`[transcodeStreamToOutput process] stderr: ${(new Date()).toISOString()} ffmpeg: ${data}`);
});

const timestamp = new Date();
const year = timestamp.getFullYear();
const month = timestamp.getMonth() + 1;
const day = timestamp.getDate();
const hour = timestamp.getUTCHours();
console.log(MEETING_ID);
const fileName = `${year}/${month}/${day}/${hour}/${MEETING_ID}.mp4`;
new S3Uploader(BUCKET_NAME, fileName).uploadStream(transcodeStreamToOutput.stdout);

// event handler for docker stop, not exit until upload completes
process.on('SIGTERM', (code, signal) => {
    console.log(`[recording process] exited with code ${code} and signal ${signal}(SIGTERM)`);
    process.kill(transcodeStreamToOutput.pid, 'SIGTERM');
});

// debug use - event handler for ctrl + c
process.on('SIGINT', (code, signal) => {
    console.log(`[recording process] exited with code ${code} and signal ${signal}(SIGINT)`)
    process.kill('SIGTERM');
});

process.on('exit', function(code) {
    console.log('[recording process] exit code', code);
});


  


  Any help would be greatly appreciated !

  


• avformat/hls : Set AVFMT_TS_DISCONT flag on HLS input format

  27 octobre 2019, par Philip Langdale

  avformat/hls : Set AVFMT_TS_DISCONT flag on HLS input format
  There have been many reports over the years about problems when
  
  taking an HLS stream as input to `ffmpeg` where there are timestamp
  
  discontinuities present. This is explicitly supported in the
  
  HLS spec (EXT-X-DISCONTINUITY) and often used for ad injection.
  Various fixes and work-arounds have been proposed over the years,
  
  but one step that seems obvious, even if it's not a complete fix,
  
  is to mark the HLS input format as supporting discontinuities. This
  
  will prevent timestamp fixup logic in ffmpeg.c kicking in that ends
  
  up mangling the timestamps unnecessarily.
  I've tested this out with an example provided by Joe Koberg early
  
  last year, and it is sufficient to allow `ffmpeg` to download and
  
  mux the stream correctly. Joe had briefly suggested that other
  
  situations can still be handled incorrectly, but this seems like
  
  a strict improvement.
  Joe's example :
  https://s3.amazonaws.com/playon-test-videos/discont_test_new/discont_test.m3u8
  Reviewed-by : Steven Liu <lq@onvideo.cn>
  
  Reviewed-by : Dennis Mungai <dmngaie@gmail.com>
  

  • [DH] libavformat/hls.c